The prior art as seen in FIG. 7 includes a piston 10 movable inside a cylinder 12 having a cylinder wall 14. The piston 10 includes a seal groove 16 in which a seal assembly 18 is positioned. The seal assembly includes a load ring 20 having a center peripheral surface 22 and oppositely disposed steps 24 on which backup rings 26 are mounted. The backup rings 26 engage the opposite sides of a seal ring 28 which in turn is in engagement with the cylinder wall 14.
Pressure from the cylinder wall 14 applied to the seal ring 28 in turn applied to the load ring 20 may cause some lateral spreading of the steps 24 but have no noticeable effect on the backup rings 26. The inner side 30 of the load ring 20 in abutment with the bottom wall of the groove 16 is flat both in its free state before assembled in a cylinder (not shown) and when assembled as seen in FIG. 7.
The object of the seal assembly is to prevent flow past the piston between the cylinder wall and the piston but also through the inclusion of the backup rings keep contaminants from reaching the seal ring 28 which would cause damage to the seal ring and the cylinder wall 14. Seal assemblies of this type and variations thereof have not been satisfactory in this regard over extended periods of use.